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Nepalese porters hit the peak of efficiency

A Nepalese porter carries a load equivalent to 100% of his body weight while his oxygen consumption is measured

(Image&colon; Science)

By Rowan Hooper

Nepalese porters are the most energy-efficient load-carriers in the world – trekking barefoot across Himalayan glaciers more than 5000 metres above sea level as they lug loads equal to their own bodyweights.

They do so with a far greater efficiency than soldiers carrying backpacks with equivalent loads, say physiologists at the Université Catholique de Louvain, in Belgium. They even beat the highly-efficient Kikuyu and Luo women of eastern Africa, renowned for carrying huge loads balanced on their heads. To find out how the Nepalese porters do it, Norman Heglund and colleagues went to the town of Namche, near Mount Everest.

“We went to these guys because they have the reputation for being the best porters,” says Heglund.

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The porters carry goods from Namche’s weekly bazaar in a basket supported by a head strap called a namlo. Heglund weighed 96 male and 17 female porters with and without their loads. The men carried an average load almost as heavy as themselves and the heaviest load was an incredible 183% of the bearer’s own weight. The women typically carried about 70% of their body weight.

The team got eight of the porters to walk around a 51 metre track at different speeds and with different loads while simultaneously measuring their oxygen consumption and carbon dioxide production. The Nepalese carried loads with greater metabolic efficiency than eastern African women and a control group of westerners carrying rucksacks. “These guys are probably approaching the limits of load-carrying abilities,” says Heglund.

Pendulum walking

The researchers expected the Nepalese porters to use a method like the Kikuyu and Luo women, who use a pendulum walking rhythm to transport loads on their heads. But the Nepalese appear to walk the same as anyone else.

Instead, it is a combination of lots of factors, says Heglund. Firstly, their diet is almost exclusively rice. The high carbohydrate intake gives the porters an efficient CO2-production to oxygen-consumption ratio – just below 1. Subjects on a more protein-rich diet have lower metabolic efficiency, says Heglund.

Secondly, the porters are small in stature. The average height of the eight experimental subjects was 1.60 m. This means they can carry proportionately higher loads, says Heglund. Thirdly, they take their time, starting before dawn and finishing after dusk, walking slowly – less than 2 kilometres per hour – and taking frequent breaks.